Wireless Communication Apparatus and a Reception Method Involving Frequency Hopping

1. A wireless communication apparatus of a direct conversion receiving scheme in which a packet is transmitted or received while performing frequency hopping for each symbol, and demodulation is started by performing carrier sensing at a beginning of the packet on a receiving side, the apparatus comprising: a plurality of receiving systems provided in accordance with a number of frequency hoppings, each of the plurality of receiving systems, setting a local oscillation frequency thereof to be fixed at a hopping frequency; and a digital baseband unit that performs carrier sensing using a predetermined number of symbols in a preamble part at the beginning of the packet, received with frequency hopping, and that performs demodulation of a payload data part after an operation from hopping pattern detection to hopping synchronization, wherein each of the receiving systems includes a variable band low-pass filter provided in a baseband portion of the receiving system, a cut-off bandwidth of the variable band low-pass filter of the receiving system being set to be a narrow bandwidth, during processing and demodulation of a portion from a preamble part to a header part.

2. A wireless communication apparatus of a direct conversion receiving scheme in which a packet is transmitted or received while performing frequency hopping for each symbol, and demodulation is started by performing carrier sensing at a beginning of the packet on a receiving side, the apparatus comprising: a plurality of receiving systems; a control unit that performs control to cause a plurality of local oscillation signals of the a plurality of receiving systems not to be frequency hopped at a time of demodulation of a portion from a preamble to a header at the beginning of the packet, the control unit performing control to cause a plurality of local oscillation signals of the a plurality of receiving systems to be frequency hopped at a time of demodulation of a payload data part to make a transition to a demodulating operation based on MIMO (Multiple Input Multiple Output) space division multiplexing.

3. The wireless communication apparatus according to claim 2 , wherein each of the receiving systems includes a variable band low-pass filter which is provided in a baseband portion of the receiving system, a cut-off bandwidth of which is set to be a narrow bandwidth during processing and demodulation of a portion from a preamble part to a header part.

4. A wireless communication apparatus of a direct conversion receiving scheme in which a packet is transmitted or received while performing frequency hopping for each symbol, and demodulation is started by performing carrier sensing at a beginning of the packet on a receiving side, the apparatus comprising: a plurality of receiving systems, a control unit that performs control to cause a plurality of local oscillation signals of the plurality of receiving systems not to be frequency hopped at a time of demodulation of a portion from a preamble to a header at the beginning of the packet, the control unit that performing control to cause the plurality of local oscillation signals of the plurality of receiving systems not to be frequency hopped also at a time of demodulation of a payload data part following the demodulation of the portion from the preamble to the header and to select, with a center frequency from among frequencies of the local oscillation signals being selected and applied in common to entire local oscillation signals of the plurality of receiving systems to perform a demodulating operation based on MIMO (Multiple Input Multiple Output) space division multiplexing.

5. The wireless communication system according to claim 4 , wherein the receiving system comprises: an analog-to-digital converter which converts an analog baseband signal to a digital baseband signal; and a digital baseband unit provided after the analog-to-digital converter, the digital baseband unit including a complex bandpass filter and a plurality of digital frequency converters, and wherein the local oscillation signals of the receiving systems are fixed at one frequency in the center of the frequencies of the local oscillation signals, and, when a symbol in a time zone where a transmission hopping frequency is a frequency other than the frequency of the local oscillation signals is demodulated, a cut-off bandwidth of the variable-band low-pass filter in each of the receiving systems is widened or narrowed to allow reception of a near zero intermediate (Near Zero IF) baseband signal responsive to a difference between the transmission hopping frequency and the frequency of the local oscillation signals after the analog-to-digital converter, the complex bandpass filter and the digital frequency converter in the digital baseband unit extracting and demodulates modulated symbols corresponding to zero frequency and positive and negative baseband frequencies.

6. A reception method of wireless communication using a direct conversion receiving scheme in which a packet is transmitted or received while performing frequency hopping for each symbol, and demodulation is started by performing carrier sensing at a beginning of the packet on a receiving side, the method comprising: setting a frequency of a local oscillator in each of a plurality of receiving systems to be fixed at each hopping frequency, the plurality of receiving systems being provided in accordance with a number of frequency hoppings; performing carrier sensing by a digital baseband unit using a predetermined number of symbols in a preamble part at the beginning of the packet received with frequency hopping; demodulating a payload data part after an operation from hopping pattern detection to hopping synchronization on the receiver; and setting a cut-off bandwidth of a variable band low-pass filter included in a baseband portion in each of the receiving systems to be narrow during processing on and demodulation of a portion from the preamble part to a header part.

7. A reception method of wireless communication based on a direct conversion receiving scheme in which a packet is transmitted or received while performing frequency hopping for each symbol, and demodulation is started by performing carrier sensing at a beginning of the packet on a receiving side, the method comprising: causing a plurality of local oscillation signals of receiving systems to be not frequency hopped at a time of demodulation of a portion from a preamble to a header at the beginning of the packet; and causing local oscillation signal of each receiving system to be frequency hopped at a time of demodulation of a payload data part, to make a transition to a demodulating operation based on MIMO (Multiple Input Multiple Output) space division multiplexing.

8. The reception method according to claim 7 , comprising setting a cut-off bandwidth of a variable band low-pass filter included in a baseband portion in each of the receiving systems to be narrow during processing on and demodulation of a portion from the preamble part to a header part.

9. A reception method of wireless communication based on a direct conversion receiving scheme in which a packet is transmitted or received while performing frequency hopping for each symbol, and demodulation is started by performing carrier sensing at a beginning of the packet on a receiving side, the method comprising: causing a plurality of local oscillation signals in a plurality of receiving systems to be not hopped at a time of demodulation of a portion from a preamble to a header at the beginning of the packet; and causing the plurality of local oscillation signals in the plurality of receiving systems to be not hopped also at a time of demodulation of a payload data part following the demodulation of the portion from the preamble to the header and selecting a center frequency from among frequencies of the local oscillation signals and applying in common to entire local oscillation signals in the plurality of receiving systems to perform a demodulating operation based on MIMO (Multiple Input Multiple Output) space division multiplexing.

10. The reception method according to claim 9 , comprising: fixing entire local oscillation signals in the plurality of receiving systems at one frequency in the center of the frequencies of the local oscillation signals; when a symbol in a time zone where a transmission hopping frequency is a frequency other than the frequency of the local oscillation signals is demodulated, widening or narrowing a cut-off bandwidth of a variable-band low-pass filter provided in a baseband portion in each of the receiving system, thereby allowing reception of a near zero intermediate (Near Zero IF) baseband signal responsive to a difference between the transmission hopping frequency and the frequency of the local oscillation signals after an analog-to-digital converter; and providing in each of the plurality of receiving systems a complex bandpass filters and a digital frequency converter in a digital baseband unit after the analog-to-digital converter, extracting and demodulating modulated symbols corresponding to zero frequency and positive and negative baseband frequencies.